Silver plating



Patented Oct. 7, 1952 raisins SHNERYJPLATING I platin'giand toIsilvenplating:baths'andhasrfor'it object to provide an electrolyte and bathca-e flenry-tewolfson'mnd Banan -Thomson, London; a Eifglahd; iassi ghors-i-to International; Standard.

, Electric: Cdi'pnra'tioinz New York, N." Y. NoiDiawingryA fplication JuiiealB; sisiiiiseri" Noi1551738'21'1 IriiGxbat BritaimJmme 2032194631 8 claims; 401. 2041446) p 2i Thisfimtentidrrrelatessstoi eleetrolytes foir silver i the" electrolyte "does not seem to betcriti'c'alzr; Most ofvour work was done with 'solutions"-containing*--: 404g. /l. of silver cyanide but we believe quite wide...: variations from this figure couldbe' tolerated; It -seems necessary (at least whileworki'n'g ,atrthepz pable of -produoing -excellent bright deposits at high:current-densitiesw anide bath containing about 40 gm. per litre of The use of potassium nitrate has been previously advocated-myPromisel anwwoodz Trans. Electrochemical Society;;l9.4= hand it .rwassclaimed that the addition of this salt tosasiivemcyanidei':

the bath and 'onth appearance of the plate; Experiments we have made---substantiated-thesei clainis, .vsemi bright depositsbeing obtained from plating solutions containing -=1-00"-l5'0"-gm. per litre' .ventional ihath couldlbe' satisfactorily worked on derr: similar" conditions was-aboutgldrama/ ti silver. Experiments we have carried out show these claims to be, in the main, justified. At an optimum concentration of potassium selenite of 0.51.5 g./l. (equivalent to 0.2-0.6 gm. of selenium vbath has a beneficial efiect on the s operation of higher current densities) to 'maintain'the custom ary' fairly high" "concentration of free cyanide?" Mostzssilver::plating;solutions:containarr.appirect ableriqu'antityrof:potassium'carbonate, but:we:pre;+2.- fercnot: .t ineludeithisisait Lass: it :appearsztozdiril minishz theczbeneficialzseffectroflthexpotassium niei trate onzseleniumx The invention is not necessarily Zliniitedvtortlrer:

addition of selenium as selenite, other soluble se- -let1ium salts .maybeioundto besuitable: i

per litre), selenium had a marked effect on the -plate and semi-bright deposits of good quality were obtained at current densities up to 28 amn/ftfi. Further experiments have led to the surprisum and potassium nitrate are, together, very distinctive and novel feature of an electrolyte,

The concentration of the other constituents of ring discovery that the two addition agents seleni- Our preferred. solutions. and-.thezrecommanded workingconditions.areasiollowsyr:2

Electrolyte-E a Electrolyte li are obtained at current densitieszof 1'8.-,-27la./ gogas im cy m 2g a i w oassumnl re. s. z' from a solution the essential feature of...which 1s Potassiumlselldite; :7 I M the addition of selemum (as seleniteytoa 'cy: Current density "amp/it 20-1130 Room temperature: Moderate agitation. Anodes-silver. two to four times area of cathode, or more.

Electrolyte A appears to yield a deposit of slightly superior quality to Electrolyte B: on the other hand Electrolyte B has a rather wider range of current density.

The ratio between the areas of the anode and cathode of a bath using an electrolyte according to the invention should be greater than that normally accepted, as otherwise anode dissolution might be impaired at the high current densities employed.

Sodium salts or other alkali metal salts may be used wholly or partly in place of potassium from which we are able to produce excellent salts on an equivalent basis. bright deposits of silver at current densities some Substantial increase of speed of deposition can four to six times greater than could be used with be obtained with a stationary cathode and withaconventional plating solution. out any form of agitation of the solution, an The formulae for our preferred solutions were node having an area about twice that of the evolved after a number of experiments aimed at cathode, and a current density of th order of determining the most useful concentration of the 10 amp/ftF, but the full advantage of the intwo addition agents. We varied the potassium Vention requires a rocking like cathode :nitrate content of the baths between 25 and 200 other method of agitation but of course without grams per litre and found a concentration of aeration, and higher current densities. With our- 100-150 g./l. to be most eifective. Potassium rent densities above 20 amp/ft an anode up to ,selenite was added in stages corresponding toga four times the area of the cathode or more will selenium content of from 0.015 to 1.0 g./l, and be required. the range 0.2-0.6 g./1. was shown to be the most By the use of the invention not only is the favourable speed of operation increased but the bright finish obtained substantially reduces or eliminates the r tion indicated:

D opor s G.- I Silver cyanide 40' Potassium cyanide 1 55 Potassium nitrate -100 Potassium selenite "1.0

2. An argentocyanide electrolyte'foruse in electrodepositing bright silver plate'athigh current densities of at least 10 amp/ft. of cathode area, that consists essentially of an aqueous solution of the following substances in substantially the proportions indicated:

G./1. Silver cyanide l 40 Potassium cyanide 55 Potassium nitrate 150 Potassium selenite 1.0

-3; An argentocyanide electrolyte for use in electrodepositing bright silverplate at high current densities of at least 10 amp/ft. of cathode area that consists essentially of anaqueous solution of the following substances in substantially the proportions indicated:

'G./l. Silver cyanide -1 40 Potassium cyanide 55 Alkali metal nitrate 100-150 Alkali metal selenite, 05 -1.5

4. An' argentocyanide electrolyte according to claim 3 in which the alkali metal nitrate is potassium nitrate and the alkali metal selenite is potas- I sium selenite. v v

5. A process for electrodepositing a bright'silver plate upon an article that comprises making the article the cathode during electrolysis at a current density of at least 10 amp/ft. of cathode area, of an electrolyte that consists essentially of an aqueou solution of the following substances in substantially the indicated proportions.

/1- Silver cyanide 40 Potassium cyanide Alkali metal nitrate -150 lAlkali metal selenite 0.5-1.5

. v 6.,Aprocess according to claim 5 in which the alkali metal nitrate is potassium nitrate and the alkali metal selenite' is potassium selenite.

7 A process according to claim 6 in which the potassium nitrate is present in the amount of 100 g./l. and the potassium selenite in the amount Of 1.0 g./1.

8. A process according to claim 6 in which the potassium nitrate is present in the amount of g./l. and the potassium selenite in the amount of" HENRY WOLFSON.

BERNARD THOMSON;

REFERENCES CITED Y The following references are of record in-the file of this'patent:

UNITED STATES PATENTS Number Name Date 2,440,672 Green May 4, 1948 1 2,449,726

OTHER REFERENCES Egeberg et al.: Transactions, or the Electro chemical Society, vol. 74 (1938), pages 211-227.

Modern Electroplating, published'1942 by the I American Electrochemical Society, pages 290, 291.'

Metallwirtschaft, vol. 22, (1945), pages 472' to 1 474, an article by Weiner.

'Ser. No; 351,241, weiner. 41." in c), published Slatkin Sept. 21, 1948' i 

1. AN ARGENTOCYANIDE ELECTROLYTE FOR USE IN ELECTRODEPOSITING BRIGHT SILVER PLATE AT HIGH CURRENT DENSITIES OF AT LEAST 10 AMP./FT.2 OF CATHODE AREA THAT CONSISTS ESSENTIALLY OF AN AQUEOUS SOLUTION OF THE FOLLOWING SUBSTANCES IN SUBSTANTIALLY THE PROPORTIONS INDICATED: 